result is called velocity head, which is used in head equations like the one used for pressure head and hydraulic head. In a venturi flow meter, the differential pressure head can be used to calculate the differential velocity head, which are equivalent in the adjacent picture. An alternative to velocity head is dynamic head. Compressible flow Many authors define dynamic pressure only for incompressible flows. (For compressible flows, these authors use the concept of impact pressure.) However, the definition of dynamic pressure can be extended to include compressible flows. For compressible flow the isentropic relations can be used (also valid for incompressible flow): Where: {| border="0" cellpadding="0" |- | style="text-align:right;" | || Mach number (non-dimensional), |- | style="text-align:right;" | || ratio of specific heats (non-dimensional; 1.4 for air at sea-level conditions), |} See also Pressure Pressure head Hydraulic head Total dynamic head Drag, lift and pitching moment coefficients Derivations of Bernoulli equation References L. J. Clancy (1975), Aerodynamics, Pitman Publishing Limited, London. Houghton, E.L. and Carpenter, P.W. (1993), Aerodynamics for Engineering Students, Butterworth and Heinemann, Oxford UK. Notes External links Definition of dynamic pressure on Eric Weisstein's World of Science Fluid dynamics